On Friday, 24 May 2013 at 06:52:19 UTC, Diggory wrote:
On Tuesday, 21 May 2013 at 20:08:16 UTC, Leandro Lucarella
wrote:
I'm interested in what you're describing, but I don't know how
can you
achieve this without fork()ing (or clone()ing in Linux). What
does
"remap shared memory using COW" in a context where fork()
doesn't
happen? Why do you even need shared memory if fork() doesn't
happen? If
"remap shared memory using COW" means get a different address
for the
same block of memory until a write happens in that block, then
you can't
scan the roots anymore.
I'm *very* interested in your suggestion.
After doing some further investigation I think I've found a
fairly awesome way of doing garbage collection on windows,
hopefully linux has a similar mechanism. It doesn't require
memory mapped files or anything special, it can be done
retroactively, and it allows a kind of reverse copy on write
which is what's actually needed.
When the GC is run:
- Use VirtualProtect to mark all mutable memory pages as
read-only
- Add a vectored exception handler to handle the access
violation exception
- Resume the GC thread
I've tried writing a generational GC for D that used page
protection for write barriers a while ago. IIRC, I ran into
performance issues (the page faults were rather expensive).
This approach does have the benefit that it will not cause pages
that have been moved to swap to be pulled out in order to be
scanned every time, though.
